Often with conventional materials, there is an inverse relationship between hardness and toughness. Generally, as the hardness of the material increases there will be a corresponding, though not necessarily proportional, decrease in the toughness of the material. On reason for this inverse relationship is because the mechanism of dislocation movement has a significant effect on both the hardness and the toughness of a conventional material. When defects are introduced into a material, the defects may tie-up dislocations, thereby preventing the material from yielding. This mechanism makes the material both harder and stronger. Conversely, removing defects from a material allows dislocations to move freely on their slip plane and slip direction producing a greater degree of ductility. From a general standpoint, resistance to cracking (i.e. toughness) will be determined by the material's ductility because stress concentrations in front of a crack tip will create a plastic zone which blunts the crack tip, reducing the stress concentration factor, thus preventing growth of the crack.
While the thermal spray coatings industry is a mature industry and the application of a high performance coatings have long been used to dramatically improve the lifetime of a part, there are many military and industrial applications for which a thermal spray coatings approach is not sufficient to solve wear problems. Problematic applications often involve heavy loads, high stress point loads, heavy impact, and gouging abrasion of the coated part. Additionally, while thermal spray may be used for limited cases in the rebuild and repair of parts, weld on techniques will generally be necessary.
Accordingly, it is an object of the present invention to provide the most efficient balance of hardness and toughness in a metallic coating, so that, in a given application, both parameters may be uniquely optimized to improve the lifetime of a part to both wear and impact type phenomena.